B_c Discovery Articles:

Physical Review Letters  (pdf format)
Physical Review D (gzipped postscript)

Information on B_c and B meson physics at CDF
General Information on the Standard Model

The Mesons and the B_c

       OK What's all this about the B_c meson? For that matter, what is a meson?
The quarks make up the protons and neutrons in  the nucleus of an atom.  But the quarks can also combine in weird ways to make up many other particles (called sub-atomic) that are not very long-lived.  Quarks will combine in groups of 3, which make up hadrons. The proton and neutron are examples of this, but there are hundreds of others involving any combinations of groups of three quarks taken among the 6 listed below.

    But the quarks will also combine with their antimatter counterparts, the anti-quarks, in pairs. These quark anti-quark pairs are called the mesons. They ALL have short lifetimes. The longest lived examples of mesons are the pions which consist of an up quark and an anti-down quark pair. They survive about 10 nanoseconds (10^-8 seconds) before decaying into a muon and a muon neutrino.

The meson that we found (Prem Singh, Junichi Suzuki, and I as part of the CDF collaboration) consists of a charm quark and an anti-bottom quark and there were only about 20 found out of 3 years of running an accelerator that achieves the highest man-made energies in the world (the Fermilab Tevatron).

This particle survives for about 0.5 picoseconds (10^-12 seconds) before it decays.

       B_c Meson properties:

Number of candidates found =  20.4^+6.2_-5.5
Discovery Channel - B_c decays to J/psi+electron (or muon)+neutrino+other stuff.
                                       The J/psi then decays to two muons, which fire the trigger.

Mass  =           Between 6.1 and 6.4 GeV/c2
Lifetime =      0.46 +/- 0.17 picoseconds
Rate Produced = 0.132 +/- 0.05  wrt B mesons decaying in a similar way.

Other properties:

Contains non-zero 'B' and 'C' quantum numbers (B = 1 and C = 1)
Ground state cannot decay through the strong or electromagnetic interactions.
Somewhere between 10% and 20% of all B_c decays will be to J/psi final states.

Updates on the B_c:

Some brief news - It looks like searches of several B_c decay modes have not turned up a sufficient signal in the Run-I CDF data to make a more precise mass measurement. I'm still hopeful that enough events will be found but as the next run of the Tevatron continues to loom ever larger I think it is more and more likely that we will wait for the higher luminosity and better vertex detector in Run-II in order to more completely study the B_c meson.

More Brief News - As of this date (08/03/01) it is pretty clear that there just wasn't any other BC signal in Run-I.  However, it is also clear that there will be loads more signal in Run-II and I expect that someone will look for this meson again. Though I expect it won't be until well into Run-II that sufficient signal worth publishing appears.

If you want an account of this from Public Relations professionals, follow this link! Otherwise...it's your own fault for reading on.

Thus far, in nature we observe only 17 particles which make up all of the matter and energy in the Universe.
They split into two broad classes that have different properties.
 

The Bosons

These particles carry the forces that cause all the interactions we observe in nature.
There are 4 known forces each has its own boson or set of bosons that will transmit this force from one interaction to the next:

1. Gravity                                    - Graviton (not yet observed directly)
2. Weak Nuclear Force          - W and Z bosons
3. Electromagnetic force        - Photon
4. Strong Nuclear Force          - Gluon

Bosons have an intrinsic quantum property called 'spin', which is a unit of angular momentum. In the case of Bosons, this angular momentum is always an integer multiple of a very small number called 'Planck's constant'.  The photon, W and Z bosons, and the Gluon all have one unit of this 'spin', while the graviton is expected to have two spin units. Some of you may have heard of the Higgs boson....if found it is expected to have zero intrinsic spin (which is also an integer multiple of Planck's constant). Oh, I will also be remiss if I do not point out that this Higgs boson is the 18th particle in this zoo, but no one has discovered it yet so it doesn't count as an 'observed' particle.

For those who want to learn a bit more:
    The Name 'Boson' comes from an Indian scientist named Bose who, with Einstein, developed the theoretical underpinnings of how these particles behave when collected together.   Prior to the 1900's, a theory of how particles behave in large numbers had been developed (largely by J.C. Maxwell and Boltzmann) that had certain successes like explaining the origin of the ideal gas law and the velocity distribution of gas molecules. What Bose pointed out was that this theory had a basic assumption that each particle in the gas was in some way distinguishable from the other particles.  In a heated gas, this is, in principle, true. Each gas molecule will have a unique momentum and energy.

   Quantum Mechanics can throw a wrench into this idea though because it tells us that no matter where anything is, there are only a finite number of possible allowed states in any given system. Therefore, in quantum mechanics, two particles could have precisely the same energy and momentum. In fact, if two particles are in the same state they must have precisely the same energy and momentum by definition. If there is no other way to tell them apart (like atoms of a single, purified gas) then the way the particles behave is quite a bit different from normal experience.

    Now in normal volumes and normal temperatures the number of available quantum mechanical states far exceeds the total number of atoms in the system. So it is very unlikely that any two will in fact have the same energy and momentum, so the system of matter or energy then looks, for all purposes, like the case where we could distinguish the particles.
    But if you take a boson-like set of particles, like helium atoms or photons, and you get them all in the same state, they behave quite differently from 'normal' matter. To do this with helium you have to cool it to very low temperatures. This reduces the total available energy and also then the states available. Eventually you will get more atoms than available states.  Super-cooled helium then behaves in a very strange ways that I am afraid I must leave you to discover. (It is a fluid with zero viscosity, for example.)

  The Fermions
 

 This Table contains a list of all known Fermions.   Just as the Bosons have an intrinsic spin, so do the Fermions, but their spin is always  n+1/2 times Planck's constant .  (OK, OK.... for those real nit-picky physicists in the bunch who REALLY should be working and not reading this, there is an additional factor of  2*pi. But that's not important for this discussion.) For all the Fermions in the table, n=0.

 

Quarks		Leptons
Name	Mass (GeV/c2)	Name	Mass
down	0.0015 to 0.005	electron neutrino	< 20 eV
up	0.003 to 0.009	electron	511.0 KeV
strange	0.06 to 0.170	muon neutrino	< 0.17 MeV
charm	1.4 +/- 0.2	muon	105.6 MeV
bottom	4.25 +/- 0.2	tau neutrino	< 18.2 MeV
top	174 +/- 6	tau	1.777 GeV

Now this spin property of being either integer or 1/2 integer multiples of Planck's constant has a profound implication that you encounter in your everyday lives. Turns out, when a particle has integer spin (boson),  one can put as many  particles in any quantum mechanical state that one wishes.  Lasers take advantage of this fact. Photons are bosons and you can just keep piling photons into exactly one state and build up a huge beam of coherent light particles.

With Fermions though, only one particle can occupy a given state at any moment.  This means that if you have a group of Fermions occupying all available states in a system, and you try to add more fermions, this will be resisted with a very strong force.

An example of this is when you stand on the floor. The fermions in the floor tiles (mostly electrons) are occupying all the available states in the floor. Now you have to realise that 'states' do not equate to 'space'. The atom is essentially entirely empty.  If the nucleus of an atom were the size of a marble, the first average position of the electron would be 100 yards away. So the floor, and your feet, are actually almost empty space. But the floor has many of its states full, so does your foot. So when you stand on the floor you are trying to force the electrons in your foot to occupy the same states as the electrons in the floor.   The floor pushes back to keep this from happening and you are prevented from sliding to the center of the earth. This repulsion is so strong that gravity only overcomes it in the formation of neutron stars after a supernova.

Fermions, because of this property, end up making all matter that we normally think about in the Universe. I can't say just 'all matter' because of something called 'dark matter' which seems to exist, but we don't know much about it....ask you local free-lance cosmologist or astrophysicist.

Even I could run-on with a diatribe about dark matter, so just imagine what an astrophysicist could do.
No, I do not intend to provide you with a link, you need to learn more about search engines anyway.

The ancient Greeks were the first who started to ask intelligent questions about what matter actually is. There were two approaches which I'm not sure were actually mutually exclusive. One approach was to assume that all matter could eventually be explained by different concentrations of  the four elements; earth, air, fire, and water. Another view asked the question, 'What is the smallest, indivisible bit, or atom, of matter?'.

The Greeks actually did a scientific experiment to try to determine how small this 'atom' was.  If you take a vial of oil and pour it on a duck pond, the oil will begin to spread out.  Eventually, before the oil begins to break up, it will always reach a certain area patch on the water's surface. The area of the final patch is always the same size if you start with the same amount of oil. Some Greek, whose name escapes me, realized that this just might be when the 'atoms' are only one-layer thick on the water's surface. The greeks figured out how big the oil molecules were using this method and got it right to within a few molecular lengths....smart guys.  Mankind has been searching for the last indivisible bit of matter, and for the true nature of the forces that direct matter's motion, ever since.

We don't call these people 'ancient Greeks' any more, they're known as 'physicists'....though I've met some who were the graduate students of the ancient Greeks.